Dr. JOE WIEMELS of UCSF explains the importance of epigenetics. Epigenetic changes do not damage DNA (like mutations), but alter when DNA is expressed. This can affect development in early life. Epigenetic changes may be a cause some types of leukemia. Leukemia includes a number of different diseases with different patterns of epigenetic markers including methylation. Environmental agents may change methylation patterns, and the changes may be heritable. This was part of a symposium organized by the Office of Environmental Health Hazard Assessment of Cal/EPA http://oehha.ca.gov/index.html, the Pediatric Environmental Health Specialty Unit at UCSF http://coeh.berkeley.edu/ucpehsu, and the Center for Integrative Research on Childhood Leukemia and the Environment at the University of California Berkeley http://circle.berkeley.edu. Research funding is from the National Institute of Environmental Health Sciences and US EPA. Views expressed are not those of these agencies.